Ferroelectric oxide thin films are of interest as dielectric materials and are useful in numerous electronic, electro-optic, and acoustical-optic applications. Ferroelectric oxide materials of interest have included both titanates and niobates which can be made as thin films by RF sputtering and more recently by organometallic chemical vapor deposition (OMCVD) as set forth by L. A. Wills et al. in "Growth studies of ferroelectric oxide layers prepared by organometallic chemical vapor deposition", Journal of Crystal Growth, 107, pp. 712-715 (1991).
There also has been considerable recent interest in the fabrication of rare earth doped thin films for optically active waveguides for integrated optics applications. Since rare earth ions exhibit a characteristic intra-4f shell luminescence emission that is both nearly host and temperature independent, rare earth doped ferroelectric oxides have been of particular interest as offering the possibility of simple optical devices that take advantage of the electro-optical and nonlinear optical (NLO) properties of ferroelectric oxides as well as the optical gain of the rare earth ions.
Optical devices, such as self-frequency-doubled, self-Q-switched, and self-modulated lasers in addition to amplified integrated optical circuits with no insertion losses are possible using rare earth doped ferroelectric oxides. Erbium-doped ferroelectric oxides have been of special interest as optically active components due the characteristic Er.sup.3+ emission at 1.54 microns, which corresponds to the minimum loss in silica based optical fibers. For example, planar waveguides and devices, including self-frequency doubled devices and lasers operating at 1.54 microns have been fabricated from rare earth doped lithium niobate (LiNbO.sub.3) bulk single crystals. Lithium niobate, however, exhibits several inherent limitations. First, the solubility of erbium ions (Er+) in the lithium niobate host material appears to be relatively low. Second, photo-refractive optical damage of the lithium niobate host can limit the efficiency and usefulness of lithium niobate based waveguides and optical devices. Third, optical waveguides comprising erbium doped lithium niobate can only be made from bulk single crystal material, which is itself difficult to make, and requires a slow, costly diffusion or ion implanation treatment to render it waveguiding and also to include the erbium dopant therein.
Copending patent application Ser. No. 08/398 419 of common inventorship and assignee herewith describes a method of making an optical working medium, such as a thin film optical wave guide, by doping a ferroelectric oxide film in-situ as it is deposited on a substrate in a reactor by OMCVD. For example, a barium-bearing reactant, titanium bearing reactant, rare earth-bearing reactant, and oxygen reactant are provided in proper proportions in the reactor and reacted under temperature and pressure conditions to deposit on a substrate, such as an oxidized silicon or a LaAlO.sub.3 substrate, a rare earth doped barium titanate film, such as Er doped BaTiO.sub.3.
An object of the present invention is to provide an optoelectronic temperature sensor comprising a doped ferroelectric oxide that exhibits a temperature dependent luminescence.
Another object of the present invention is to provide an optoelectronic temperature sensitive signal-generating device that monitors the change in luminescence intensity of a doped ferroelectric oxide with temperature changes and provides a temperature dependent electrical signal representative of temperature change.